The state of the art for cryogenic concrete cooling is well documented in WO 2006/100550 as filed by Air Liquide. As noted in WO 2006/100550, when preparing concrete it is often necessary to cool the concrete mix since the structural integrity of the resulting concrete is dependent upon the temperature at which the concrete is set. Typically, the cooler the concrete when poured, the stronger it will be once it is set. Concrete that is poured at high temperatures will often not meet the minimum strength requirements, especially in warm weather climates.
In the past, this issue was addressed in a number of ways including 1) cooling the water used in mixing the concrete using a refrigeration unit, ice, or a cryogenic liquid which was mixed with the water before mixing the concrete and 2) injecting a cryogenic liquid directly into a concrete mixer drum of a truck while it is being mixed in a conventional rotating mixer. The first approach was found to present problems in terms of cost, timeliness, labor intensity, additional equipment, safety issue and final product issues. The second approach was found to present problems because of potential damage to the truck mixer drum.
Furthermore, the prior art systems basically fall into one of two main categories: those that are manually operated and those that are automated. Each has its own advantages and disadvantages with regards to fabrication cost, fabrication time, set-up/breakdown difficulty, operation (achievable productivity, safety, required training, ease of use, etc.), maintenance, storage, useful life, etc. The manually intensive systems are typically lower in cost, but are less productive and less safe. These systems involve manually positioning and clamping a lance to the concrete mixing drum before allowing the cryogenic liquid (e.g., nitrogen) to flow. Once the cooling process is complete, it is necessary to then unclamp and remove the lance, once again by hand. The highly automated systems are more productive and safer to operate, but they have a higher cost to manufacture and maintain. With these systems, the positioning and cryogenic liquid flow is controlled with various electric and/or pneumatic actuators so that no manual intervention is required.
While multiple prior art systems have sought to overcome the issues associated with these systems by providing relatively inexpensive systems that adjust to accommodate the relative position and particular specifications of a given container without so much manual intervention, there are still problems with these systems. For example, systems such as those disclosed in WO 2006/100550 use pneumatic cylinders to control the lance insertion and retraction due to the required length of travel of about five (5) feet or more. The cylinder can be controlled to either fully extend or to either fully retract, but are not capable of partially extending/retracting. Once the signal to extend the lance is given, the operator can only stop the lance by activating an emergency stop. If the lance or truck is positioned in a way so as to introduce a collision hazard, the operator often does not have enough time to react to prevent a collision. This collision often results in lance or mixer damage and often causes the lance to detach from the pneumatic cylinder. When the lance is detached, it must be manually returned to its proper position which results in significant down time. The practice of returning the lance to its original position is complicated since it often requires additional manpower and equipment to complete the task.
Also, while systems such as those disclosed in WO 2006/100550 do disclose a system that provides a lance that is capable of movement with a certain degree of freedom, such freedom is accomplished through the use of multiple actuators that act on the lance which must be coordinated in their workings in order to provide the degree of movement necessary without harming the lance and/or the mixer drum.
Accordingly, there exits a need for a system that includes the benefits of fully automated systems, including a great degree of freedom of movement of the lance, while at the same time simplifying the overall design. Concrete cooling using an automated injection system is desirable because it is safer and allows for increased productivity. The more complex a device is, however, the more expensive it is to fabricate and maintain. In addition, complexity negatively affects fabrication, installation, and removal lead times, which adds to the cost of operation. It is therefore the objective of the present invention to provide a system that is simple in design, inexpensive to make and easy to install, remove and maintain. It is the further objection to provide a system that eliminates damage to the lance device, particularly the rigid lance, in situations where the concrete mixer truck is repositioned before completion of the injection of the cooling fluid.